Fig. 9. Model for synergistic action of TORC2 inhibition and Zeocin driving fragmentation.

A mechanistic model of how TORC2 inhibition impacts base excision repair to generate rapid and irreversible DSBs in yeast. Related imidazoquinolines CMB4563 and NVP-BHS345 inhibit TORC2^34,35 and in turn YPK1/YPK2, which inactivates Alk1, Prk1 and Ark1^34,36,37. These kinases lead to the disruption of several actin regulatory complexes that primarily downregulate endocytosis but also lead to Las17 inactivation and partial relocation to mitochondria. TORC2 inhibition, like the degradation of Las17, leads to increased availability of non-filamentous globular actin (G-actin) and its nuclear accumulation. In Zeocin-treated yeast, the presence of enhanced levels of nuclear actin could activate actin-dependent nucleosome remodelers such as INO80C to increase endonuclease access at paired base oxidation events on opposite strands³⁵ (as shown) and increase DNA polymerase processivity^40–45. When the processive replication polymerase meets a single-strand break created by premature Apn1 (or Ogg1) activity, DSBs can form ref. ³⁵. Our results suggest a role for chromatin in the appropriate coordination of repair of clustered oxidative lesions.